1. Field of Invention
The invention relates to a racket stringing machine structure and, in particular, to a stringing device of a racket stringing machine.
2. Related Art
As shown in FIG. 7, the stringing device of a racket stringing machine in the prior art has the following structure. A stringing head 72 is disposed on the top surface of a sliding base 71. The sliding base 71 is mounted on two guiding rails 73 in parallel. The sliding base 71 is connected with a chain 75 winding around two gears 74. A driving motor 76 drives one of the gears 74 to pull the chain 75, thereby pulling the sliding base 71 to move in a straight line along the guiding rails 73.
In the above-mentioned stringing device of a racket stringing machine, the sliding base 71 slides on the guiding rails to pull a string. To ensure the smoothness of the sliding base 71 as it slides, it usually requires high precision between the sliding base 71 and the guiding rails 73. Since there is a certain string-pulling distance, the guiding rails 73 have to a sufficient length. This renders the precision control even more difficult, thus increasing the production cost. Moreover, in addition to the transmission structure for pulling the sliding base 71, the stringing device further has the structure of guiding rails that go through the sliding base 71. Such a structure makes the size of the stringing device larger.
To reduce the production cost, U.S. Pat. Nos. 4,620,705, 5,733,212, and 6,227,990 proposed to use a screw bar to drive the sliding base installed with a stringing head structure. However, in these patents, as the screw bar drives the sliding base, the force to pull the string may tilt the sliding base relative to the screw bar. Therefore, the screw bar can be easily deformed or worn out too quickly.